1. Technical Field
The present disclosure relates to a method, an apparatus and a use of an apparatus for proving an authentication of an original item as well as to a hereto related method and apparatus for determining an authentication status of a suspect item. The disclosure further relates to a computer program for performing the mentioned methods as well as to a data carrier having a data structure stored thereon, which, after loading into a computer or a computer network, is capable of executing the methods.
2. Description of the Related Art
The proof of the authentication of an original item as well as the determination of the authentication status of a suspect item based on an evaluation of material structures and/or production tolerances is a well-known technology which has been largely developed during the last decades. The basic methods in this field have been triggered by the authentication proof and determination of bank notes, commercial papers and/or security documents. Within this regard, a number of authentication methods and devices have been described which mainly rely on a recognition of unique features emerging during a production process in order to be able to determine the authentication status of a suspect item. These kinds of technologies are usually based on the observation that a substrate, such as a paper or a cardboard, due to its organic and anisotropic material structure, generally absorbs inks locally in an individual manner, by which process non-reproducible patterns may evolve throughout the area wherein the ink is absorbed, particularly at the margins of such areas.
The first concepts for determining these kinds of structures, however, had to struggle with various barriers which mainly concerned the processing and storing of data related to the authentication status. For example, as described in U.S. Pat. No. 4,423,415; U.S. Pat. No. 4,811,408, and U.S. Pat. No. 4,837,840; patterns determined from such unique structures were generally printed on the documents themselves in the form of a barcode and/or stored in a magnetic memory which forms part of the respective document. However, both the technological barriers concerning the reproducibility of the recognition of unique features as well as the insufficient storing capabilities led to a security problem which complicated the generation of authenticatable documents.
U.S. Pat. No. 5,521,984 discloses a method for determining an authentication status of a suspect item particularly applicable to objects of fine art, including limited edition prints, and which is based on the uniqueness of actions involved in the creation of such an object, e.g. a brush stroke exerted by an artist. Hereby, the authentication of the original item is determined by recording at a microscopic level a unique pattern of such a feature at a selected microsite of the original item which is subsequently stored in a central data storage from which it can be retrieved over a communication link upon request and compared with an actually recorded picture of the same microsite of the suspect item.
Particularly owing to the considerable developments in the fields of imaging and storing technologies, various advanced systems which are capable of the recognition of structures have been proposed. Within this regard, devices for the generation of hardly reproducible print images have been introduced, which make use of principle of lossy reproduction in order to enable a determination of the authentication status of a document (see, e.g. EP 1319291 B1, EP 1514227 B1, WO 2006/013037 A1, US 2010/0027851 A1, U.S. Pat. No. 7,080,041 B2). Herein, deviations within the print images are recognized on a micro-scale and stored for retrieving and comparing within a further authentication process. In general, the storing takes place in a database which comprises the various print images and/or information related to their specific uniqueness. As a result, this kind of procedure generates large databases which have to be searched completely during an authentication process. In order to achieve a high reliability of the authentication process, on one hand, an acquisition of print images with a high resolution is required and, on the other hand, large efforts are needed in order to allow a rapid browsing of the database. As an alternative, U.S. Pat. No. 6,550,685 B1 therefore proposes to extract unique features from the print image and print it separately in the form of a code onto the same item.
A further example may be found in WO 2013/130946 A1, wherein natural variations in marked features on an item, such as a barcode oriented onto the item, are assessed with respect to artifacts which are specific to the item. For this purpose, information associated with the artifacts is extracted, whereupon the information is ranked according to characteristics of the artifacts, in particular by calculating an autocorrelation series of the ranked information. Hereby, ranking includes treating artifacts with a characteristic below a threshold differently from artifacts above the threshold, such as not ranking artifacts smaller than the threshold, or grouping artifacts together with locations where no artifact is detected, or discounting artifacts. Thereafter, the ranked information or data representing the autocorrelation series are stored in a storage device separate from the original item.
Various devices and methods employ laser systems which are primarily used in order to record not the printed documents themselves but rather the irregularities within the substrate materials utilized to carry the printed information (see, e.g. DE 101 55 780 A1, DE 101 62 537 A1, U.S. Pat. No. 7,089,420 B1, WO 2007/072044 A1, WO 2008/059017 A1, U.S. Pat. No. 7,599,544 B2, WO 2010/070345 A1).
Other known methods make use of already existing print images or invisible marks on the object (see, e.g. EP 1319219 B1, EP 1 433 305 B1, EP 1 690 697 A1). Within this regard, irregularities which occur during a printing process on a micro-scale, particularly through a dispersion of inks, by vibrations of the printing equipment, or through other effects such as partially blocked nozzles, are employed in the authentication process. As an example, DE 10 2008 007731 A1 and U.S. Pat. No. 7,533,062 B2 describe a method and a device for authenticating items by carefully recording the margins of printed areas from which an identifiable signature is determined which is used for further authentication of the suspect item.
O. Bulan and G. Sharma, High Capacity Color Barcodes: Per Channel Data Encoding via Orientation Modulation in Elliptical Dot Arrays, IEEE Transactions on Image Processing, Vol. 20, pp. 1337-1350, 2011, present a new high capacity color barcode. The barcode uses the cyan, magenta, and yellow (C, M, Y) colorant separations available in color printers and enables high capacity by independently encoding data in each of these separations. In each colorant channel, payload data is conveyed by using a periodic array of elliptically shaped dots whose individual orientations are modulated to encode the data. The orientation based data encoding provides beneficial robustness against printer and scanner tone variations. The overall color barcode is obtained when these color separations are printed in overlay as is common in color printing. A reader recovers the barcode data from a conventional color scan of the barcode, using red, green, and blue (R, G, B) channels complementary, respectively, to the print C, M, and Y channels. For each channel, first the periodic arrangement of dots is exploited at the reader to enable synchronization by compensating for both global rotation and scaling in scanning and local distortion in printing. To overcome the color interference resulting from colorant absorptions in non-complementary scanner channels, a novel interference minimizing data encoding approach and a statistical channel model (at the reader) that captures the characteristics of the interference are proposed, enabling more accurate data recovery. Further, an error correction methodology that effectively utilizes the channel model is employed.
O. Bulan, J. Mao, and G. Sharma, Geometric distortion signatures for printer identification, 2009 IEEE International Conference on Acoustics, Speech and Signal Processing, pp. 1401-1404, 2009, present a forensic technique for analyzing a printed image in order to trace the originating printer. This method, which is applicable for commonly used electro-photographic (EP) printers, operates by exploiting the geometric distortion that these devices inevitably introduced in the printing process. In the proposed method, first a geometric distortion signature is estimated for an EP printer. This estimate is obtained using only the images printed on the printer and without access to the internal printer controls. Once a database of printer signatures is available, the printer utilized to print a test image is identified by computing the geometric distortion signature from test image and correlating the computes signatures against the printer signatures in the database. Experiments conducted over a corpus of EP printers demonstrate that the geometric distortion signatures of test documents exhibit high correlation with the corresponding printer signatures and a low correlation with other printer signatures.
Although various methods and devices for determining the authentication status of a suspect item have been proposed, still, a number of problems and obstacles exist which particularly impede their industrial implementation on a larger scale. Within this regard, a major issue relates to the resolution of optical systems which are employed in the acquisition of print images such as one- or two-dimensional barcodes. In order to assess the irregularities at the margins of a print image, an optical system with a resolution and a magnification being at least comparable to the size of the print irregularities is required. As a result, however, an optical system comprising both a high resolution and a high magnification must be employed. As an example, the modules of a two-dimensional barcode, such as a data matrix barcode, are usually decoded in industrial facilities by employing an optical system which comprises a resolution of 5 pixels per dimension. However, in order to resolve the margins of the modules of the barcode with sufficient resolution, 40 pixels per dimension are needed. However, this requirement which increases the resolution of the optical system by a factor of 8 in each dimension leads to an increase of the data volume to be further processed by a factor of 64. Consequently, the requirements on the optical system as well as on the data storage system are multiplied in a system which is configured for assessing margins of a print image compared to a device being adapted for simply decoding a two-dimensional barcode. As a result, devices which are already installed for the decoding of barcodes do not exhibit a sufficient resolution which would allow employing such devices for the recognition of irregularities in the margins of a print image at the same time. In other words, existing optical systems have to be upgraded in order to be able to perform a margin analysis of print images within the determination of the authentication status of a suspect item.
In addition, such methods and devices for determining the authentication status of a suspect item require a high sharpness of the print image. Together with the high resolutions and, additionally, high processing speeds, which could be up to 2000 recordings per minute, very short exposure times are required in order to record pictures which exhibit only a slide motion blurring, particularly in a range below two pixels. Comparing these requirements with known decoding systems for barcodes which employ an exposure time of approximately 1:8 000 s, an exposure time of 1:80 000 s would be necessary. This would require a high illumination which is rather sophisticated and lead to a large heat generation which could heat up the object to intolerable values. Consequently, methods and devices for determining the authentication status of a suspect item which are based on margin recognition are currently not compatible with the requirements in industrial facilities.